The present invention relates to a method for cleaning pressurized containers having chemicals contained therein. Specifically, the present invention relates to a method of cleaning pressurized containers such as, for example, rail tank cars, mobile tanks or the like. Further, the chemicals stored within the containers specifically relate to liquefied petroleum gas that may include, but not be limited to, a plurality of hydrocarbon molecules specifically defined herein.
It is, of course, generally known to store and/or transport chemicals having hazardous characteristics via pressurized containers. Further, it is also generally known to clean these containers using a variety of methods and systems. In the past, cleaning pressurized containers entailed venting excess gaseous material to the atmosphere. Further, unpressurized containers contained bottom hatches or valves for draining liquid chemicals. However, many hazardous chemicals escaped into the environment thereby causing health risks for humans, vegetation and wildlife. With the advent of environmental standards and compliance, however, venting or draining hazardous chemicals to the environment has generally become illegal. Today, the chemicals are typically routed to a flare to be incinerated or otherwise collected for disposal.
However, while some of the gases contained within the containers may be relatively easy to recover and dispose of by venting of the pressurized containers to a flare, it is difficult to remove all of the gases contained therein. Further, liquid product may remain inside a container after cleaning. Typical systems and methods of cleaning may involve injecting the container with a quantity of steam that may aid in bringing the liquid chemicals to the gaseous phase and removing the steam/gaseous chemical product combination for incineration or disposal. However, problems may occur using steam to remove chemicals from pressurized containers since steam may condense within the container forming liquid water or ice. The liquid water or ice may mask the presence of the chemicals from detectors. Further, the liquid water or ice may interfere with the removal of the chemicals from the container.
Another method of removal, especially for unpressurized containers having liquid therein, may include entering the container to manually remove the chemical. While this may be a relatively efficient and thorough way to remove the chemical from the container, it may be very dangerous, as it requires an individual to actually enter the container thereby exposing the individual to the chemicals contained therein. Further, by opening the container, there may be a significant risk that some of the chemicals may escape into the environment.
Therefore, an improved system of cleaning pressurized containers is necessary. Particularly, a system is needed that overcomes the problems associated with typical cleaning systems. Further, a system is needed that cleanly and efficiently moves chemical product from a pressurized container and transports the waste product to a proper disposal system such as a flare for incineration.
The present invention relates to a method of cleaning a pressurized container having chemicals therein. More specifically, the present invention allows containers such as, for example, rail tank cars, to be cleaned safely and efficiently without risking exposure of the chemicals to people or the environment. The invention entails injecting heated and pressurized nitrogen gas into the container thereby purging the container of any chemical therein to form a nitrogen/chemical mixture. The nitrogen/chemical mixture may then be sent to a flare for incineration. Further, the heated nitrogen gas may aid in pulling the chemical out of the container and transporting the chemical to the flare for incineration.
To this end, in an embodiment of the present invention, a method of cleaning a pressurized container is provided. The method comprises the steps of providing a pressurized container containing an amount of liquefied petroleum gas wherein the container has inlet and outlet valves and injecting a quantity of heated nitrogen gas onto the container to form a nitrogen/liquid petroleum gas mixture. Further, the method comprises venting the nitrogen/liquid petroleum gas mixture to the flare and repeating injecting the container with heated nitrogen gas and venting the mixture to the flare until the concentration of liquid petroleum gas reaches a predefined limit.
In an embodiment of the present invention, the predefined limit is less than or equal to about 50 percent of the lower explosion limit for the liquefied petroleum gas.
In an embodiment of the present invention, the method comprises the steps of visually inspecting the container for leaks and providing a housing having a cover on the wherein the housing has a plurality of valves therein and a plurality of sideports for access to the interior of the dome. Further, the method comprises sampling the interior of the housing via the sideport for a quantity of liquid petroleum gas via a chemical detecting instrument for leaks and removing the cover of the housing to inspect the interior of the dome for leaks.
In an embodiment of the present invention, the method comprises the steps of weighing the container and comparing the weight of the container to a tare weight of the container to determine a weight of the liquid petroleum gas therein.
In an embodiment of the present invention, the method comprises the steps of attaching a nitrogen line between a nitrogen tank and a first valve of the container and allowing nitrogen gas to flow from the nitrogen tank to the container. The method further comprises heating a portion of the nitrogen line to heat the nitrogen gas contained within the nitrogen line and attaching a fare line between the container and a flare.
In an embodiment of the present invention, the method comprises the steps of sampling a quantity of liquid petroleum gas in vapor form to determine a concentration of vapor within the container and verifying the identity of the liquid petroleum gas within the container.
In an embodiment of the present invention, the method comprises the steps of the nitrogen gas is heated to between about 100xc2x0 F. and about 300xc2x0 F.
In an embodiment of the present invention, the method comprises the steps of inspecting the container for leaks via a leak detection apparatus and stopping the cleaning of the container if a leak is found having a concentration of at least about 10% of the lower explosion limit of the liquid petroleum gas.
In an embodiment of the present invention, the method comprises the steps of injecting the heated nitrogen into the container via a vapor valve on the container and venting the gas within the container to the flare via one of the valves.
In an alternate embodiment of the present invention, a method of cleaning a pressurized container is provided. The method comprises the steps of providing a pressurized container having an amount of liquid petroleum gas therein wherein the container has a plurality of valves and injecting a quantity of heated nitrogen gas into the container to form a nitrogen/liquid petroleum gas mixture. Further, the method comprises venting the nitrogen/liquid petroleum gas mixture to a flare and repeating injecting the container with the heated nitrogen gas and venting the mixture of the flare until the concentration of the liquid petroleum gas reaches about 0% of the lower explosion limit of the liquid petroleum gas.
In an embodiment of the present invention, the method comprises the step of inspecting the container for leaks.
In an embodiment of the present invention, the method comprises the steps of inspecting the container for leaks via a leak detection apparatus and stopping the cleaning of the container if a leak is found having a concentration of at least about 10% of the lower explosion limit of the liquid petroleum gas.
In an embodiment of the present invention, the method comprises the steps of visually inspecting for leaks in the container and providing a housing having a cover and an interior space wherein a plurality of valves are contained within the interior space. The method further comprises providing at lest one sideport in the housing for accessing the interior space of the housing, sampling the interior of the housing via the sideport for a leak in the plurality of valves via a chemical detection device, and removing the cover to inspect the interior space of the dome for leaks.
In an embodiment of the present invention, the method comprises the steps of weighing the container and comparing the weight of the container to a tare weight of the container to determine a weight of the liquid petroleum gas therein.
The method of claim 10 further comprising the steps of attaching a nitrogen line between a nitrogen tank and a first valve of the container, heating a portion of the nitrogen line to heat nitrogen contained within the nitrogen line, and attaching a flare line between the container and a flare.
In an embodiment of the present invention, the method comprises the step of sampling a quantity of liquid petroleum gas contained in the headspace of the container to determine a concentration of the liquid petroleum gas within the headspace.
In an embodiment of the present invention, the nitrogen gas is heated to between about 100xc2x0 F. and about 300xc2x0 F.
In an embodiment of the present invention, the method comprises the steps of injecting the heated nitrogen into the container via a vapor valve on the container and venting the case within the container to the flare via a liquid valve on the container.
In an embodiment of the present invention, the method comprises the step of injecting the container with steam after the concentration of the liquid petroleum gas therein is about 0% of the lower explosion limit of the liquid petroleum gas.
In an embodiment of the present invention, the method comprises the steps of providing a pressure plate on the container for gaining access to the container, removing the pressure plate on the container, entering the container, and cleaning debris from the container.
It is, therefore, an advantage of the present invention to provide a method of cleaning a pressurized container having a quantity of chemicals therein that safely and efficiently removes chemicals from the container. Moreover, it is advantageous that the present invention removes chemicals from the container without risking exposure to people or the environment.
Further, it is an advantage of the present invention to provide a method of cleaning a pressurized container having a quantity of chemicals therein that allows the chemicals to be removed without causing damage to the container by freezing the container or pipes connected thereto. In addition, an advantage of the present invention is that the heated nitrogen gas used to remove the product will not condense within the container and therefore will not mask the presence of the chemicals therein.
Another advantage of the present invention is to provide a method of cleaning a pressurized container having a quantity of chemicals therein that is largely automatic and therefore allows an individual to monitor the process without exposing the individual to the chemicals. Additionally, an advantage of the present invention is that a plurality of types of containers may be cleaned using the system and method defined herein, including, but not limited to, rail tank cars and other like containers.